Another possibility which this extension provides is 'making window
always visible' (i.e. always on current workspace), similar to corresponding
metacity functionality. This behaviour is emulated through copying given
window to all the workspaces and then removing it when it's unneeded on
all workspaces any more.

runOrCopy will run the provided shell command unless it can
find a specified window in which case it will copy the window to
the current workspace. Similar to (i.e., stolen from) XMonad.Actions.WindowGo.